A selection of cobalt(I) and cobalt(II) pincer type complexes with different substitution patterns was tested in the catalytic reduction of carboxylic acid esters to alcohols. The cobalt pincer type complex 4 is suitable for the hydrogenation of aromatic as well as aliphatic and cyclic esters. Mechanistic investigation indicated a metal ligand cooperated reaction pathway.

DFT has been used to investigate viable mechanisms of the hydrogen evolution reaction (HER) electrocatalyzed by [Fe(CN){μ-CN(Me)}(μ-CO)(CO)(Cp)] (1) in AcOH. Molecular details underlying the proposed ECEC electrochemical sequence have been studied, and the key functionalities of CN and amino-carbyne ligands have been elucidated. After the first reduction, CN works as a relay for the first proton from AcOH to the carbyne, with this ligand serving as the main electron acceptor for both reduction steps. After the second reduction, a second protonation occurs at CN that forms a Fe(CNH) moiety: i.e., the acidic source for the H generation. The hydride (formally 2e/H), necessary to the heterocoupling with H is thus provided by the μ-CN(Me) ligand and not by Fe centers, as occurs in typical LFeS derivatives modeling the hydrogenase active site. It is remarkable, in this regard, that CN plays a role more subtle than that previously expected (increasing electron density at Fe atoms). In addition, the role of AcOH in shuttling protons from CN to CN(Me) is highlighted. The incompetence for the HER of the related species [Fe{μ-CN(Me)}(μ-CO)(CO)(Cp)] (2) has been investigated and attributed to the loss of proton responsiveness caused by CN replacement with CO. In the context of hydrogenase mimicry, an implication of this study is that the dithiolate strap, normally present in all synthetic models, can be removed from the Fe core without loss of HER, but the redox and acid-base processes underlying turnover switch from a metal-based to a ligand-based chemistry. The versatile nature of the carbyne, once incorporated in the Fe scaffold, could be exploited to develop more active and robust catalysts for the HER.

Novel Ru–NHC complexes bearing cyclopentadienones/hydroxycyclopentadienyls are active and selective in transfer hydrogenation exploiting the cooperation of both classes of ligands.

Novel iron complexes bearing both cyclopentadienone and N-heterocyclic carbene ancillary ligands were obtained by a straightforward synthesis from Fe2(CO)9. The preparation represents a rare example of silver transmetallation involving iron. The reaction is general and occurs in the presence of variously functionalized NHC and cyclopentadienones.

The peculiar reactivity of catechol carbonate (CC) with amines and polyamines in both solvent-and catalyst-free conditions is herein described. In all the tests performed at room temperature, CC conversion reached 100% in a few seconds leading to the selective formation of the corresponding 2hydroxyphenylcarbamate. This compound is further rapidly converted to the disubstituted urea by the consecutive nucleophilic attack of another amine. Noteworthy, the application of this approach can be successfully extended to the one-pot bioaminebased synthesis of polyurea as herein proposed for the first time in the literature. The reaction is of general purpose for primary amines, and catechol can be easily recovered by sublimation as pure crystals ready to be recycled for the synthesis of new CC. An exception is related to the reactivity of secondary amine, which leads to the selective formation of substituted phenolic carbamates (e.g., 2-hydroxyphenyl diethylcarbamate), suitable as intermediates in medicinal chemistry.

The reactivity of the dinuclear complex dicarbonyl[η4‐3,4‐bis(4‐methoxyphenyl)‐2,5‐diphenylcyclopenta‐2,4‐dienone] (2) with imidazolium salts has been studied using a library of variously functionalized imidazolium salts, and leading to a class of ruthenium anionic complexes of the type [dicarbonyl{η4‐3,4‐bis(4‐methoxyphenyl)‐2,5‐diphenylcyclopenta‐2,4‐dienone} (halide)Ru][1,3‐disubsittuted‐imidazolium] (4) in the form of ion pair with imidazolium. The reaction is clean, general and quantitative and the complexes formed are stable to air and moisture both in the solid state and in solution. The ionic complexes 4 show affinity for ionic liquids and represent stable precursors of a catalytic active species, likely similar to those generated from Shvo catalyst, a well‐established homogeneous bifunctional catalyst for hydrogen transfer. Our approach allows the use of green ionic liquids (IL) as solvents, providing better control of catalytic reactions involving 4, and easier catalyst recycle. IL‐supported ionic pair catalysts exhibit interesting catalytic activity (up to > 99 % of conversion) in the transfer hydrogenation of a model compound such as 4‐fluoroacetophenone. The IL‐supported redox catalysts can be also recycled exploiting the biphasic nature of the system. The synthetic method here discussed represents a novelty within the field of IL‐supportation and is potentially useful for the heterogenization of the catalysts.

Iron(II) bis-pyrazolilpyridyl (bpp-R) complexes [Fe(bpp-R)2](X)2·solvent, R = substituent and X– = anion, can undergo spin transition from high (S = 2, HS) to low spin (S = 0, LS), being...

The cover image is based on the Full Paper Synthesis, reactivity and preliminary biological activity of iron(0) complexes with cyclopentadienone and amino‐appended N‐heterocyclic carbene ligands by Andrea Cingolani et al., https://doi.org/10.1002/aoc.4779. Illustration Credit: Rita Mazzoni and Elena Gigli.